enable spotlight indexing for FAT32

It seems to be impossible to enable/disable spotlight indexing status for a FAT32 volume when root is being indexed:

If indexing status can't be set:
~$ sudo mdutil -i on /Volumes/FAT32/
Could not set indexing status for volume.

Solve the problem by:
~$ sudo mdutil -i off /
Indexing disabled for volume.

Then enable those drives you want to be indexed:
~$ sudo mdutil -i on /Volumes/FAT32/
Indexing enabled for volume.
~$ sudo mdutil -i on /Volumes/Macintosh\ HD/
/Volumes/Macintosh HD/:
Indexing enabled for volume.

or try http://www.fixamacsoftware.com/software/spot/